1. Field of the Invention
The invention relates to a cold storage device, particularly, for use with an automobile air conditioning system, whereby the temperature of a vehicle interior can be cooled more quickly.
2. Description of Related Art
Despite high-performance air-conditioning systems, the air conditioning of automobiles still lacks a certain level of comfort, because at high external temperatures and/or in strong sunshine the vehicle interior is often at a high temperature when the occupant first enters the vehicle. Therefore, a certain period of time is required after starting the vehicle before a pleasant temperature is reached in the vehicle interior. In order to reduce this cooling time and to cool the vehicle interior more quickly, cold storage devices, which are able to release very high cooling capacities within a short time, are utilized.
There are essentially three core problems that have to be solved when designing cold storage devices. It is necessary to provide a good level of heat transfer from a storage medium to a heat transfer medium, to design an effective cold storage device under extreme space constraints due to the compactness of vehicles, and to avoid bursting problems.
The storage medium, which is typically water, should be supercooled only slightly before it starts freezing. Moreover, it is necessary to accommodate expanding volumes due to an expansion of the storage medium when the temperature changes. More particularly, the change in volume caused by phase change is of central importance, because a volume expansion can quickly cause the accumulator to be damaged or possibly destroyed. For example, water expands when it is frozen, therefore , when it is used as the storage medium there is a heightened risk of damage due to water's changing volume.
Cold storage devices are already being used in stationary air-conditioning technology. In this sector, the risk of the storage device bursting due to volume expansion caused by the storage medium freezing is countered by using containers with a suitably large volume which are only partially filled with the storage medium. Such designs cannot be employed in automotive engineering, because of a lack of sufficient space in vehicles and the associated demand for compact designs, and because of the extreme climatic conditions to which a vehicle may be exposed and which the accumulator has to withstand.